Oxycodone, morphine, and other opioid analgesics are therapeutically useful and effective medications, e.g., as pain killers, when administered orally. Unfortunately, they also pose a severe threat for willful abuse due to their ability to alter mood and/or cause a sense of euphoria. Currently available sustained release formulations of such drugs, which contain a relatively large amount of drug intended to be released from the formulation over an extended period of time, are particularly attractive to abusers since the sustained release coating can be destroyed by crushing or grinding the formulation. The crushed material no longer controls the release of drug. Depending on the drug, abusers can then (1) snort the material, (2) swallow the material or (3) dissolve the material in water and subsequently inject it intravenously. The dose of drug contained in the formulation is thus absorbed immediately through the nasal or GI mucosa (for snorting or swallowing, respectively) or is administered systemically in a bolus via the circulatory system (for IV injection). These abuse methods result in the rapid bioavailability of relatively high doses of drug, giving the abuser a “high”. Since relatively simple methods (crushing, grinding, chewing and/or dissolution in water) can be used to transform such formulations into an abusable form, they provide virtually no deterrent to a potential abuser.
For example, the FDA recently strengthened the warnings and precautions sections in the labeling of OxyContin® (oxycodone HCl controlled-release) tablets, a narcotic drug approved for the treatment of moderate to severe pain, because of continuing reports of abuse and diversion. OxyContin®, contains oxycodone HCl (available in 10, 20, 40 and 80 mg strengths), an opioid agonist with an addiction potential similar to that of morphine. Opioid agonists are substances that act by attaching to specific proteins called opioid receptors, which are found in the brain, spinal cord, and gastrointestinal tract. When these drugs attach to certain opioid receptors in the brain and spinal cord they can effectively block the transmission of pain messages to the brain. OxyContin® is supplied in a controlled-release dosage form and is intended to provide up to 12 hours of relief from moderate to severe pain. The warning specifically states that the tablet must be taken whole and only by mouth. When the tablet is chewed or crushed and its contents are swallowed, snorted into the nostrils or dissolved and subsequently injected intravenously, the controlled release mechanism is destroyed and a potentially lethal dose of oxycodone becomes bioavailable.
In recent years, there have been numerous reports of Oxycodone diversion and abuse in several states. For example, DEA's Office of Diversion Control reported 700 OxyContin® thefts in the U.S. between January 2000 and June 2001. Some of these reported cases have been associated with serious consequences including death.
Oxycodone is a controlled substance in Schedule II of the Controlled Substances Act (CSA), which is administered by the Drug Enforcement Administration (DEA). Despite the fact that Schedule II provides the maximum amount of control possible under the CSA for approved drug products, in practice, it is difficult for law enforcement agencies to control the diversion or misuse of legitimate prescriptions. Although abuse, misuse, and diversion are potential problems for all opioids, including Oxycodone, opioids are a very important part of the medical arsenal for the management of pain when used appropriately under the careful supervision of a physician.
Currently available formulations for such drugs are designed for oral administration but do not include mechanisms to prevent or retard improper methods of administration such as chewing, injection and snorting. This represents a serious problem given the large number of legitimate prescriptions written in the U.S.; for example, the medical use of opioids within the U.S. increased 400% from 1996 to 2000. The problems with abuse are significant and longstanding, and efforts to design new abuse-resistant or abuse-deterrent formulations have been largely unsuccessful. U.S. Pat. Nos. 3,980,766, 4,070,494 and 6,309,668 describe formulations designed to prevent the injection of compositions meant for oral administration. U.S. Pat. No. 3,980,766 describes the incorporation of an ingestible solid which causes a rapid increase in viscosity upon concentration of an aqueous solution thereof. U.S. Pat. No. 4,070,494 describes the incorporation of a non-toxic, water gelable material in an amount sufficient to render the drug resistant to aqueous extraction. U.S. Pat. No. 6,309,668 describes a tablet for oral administration containing two or more layers comprising one or more drugs and one or more gelling agents within separate layers of the tablet. The resulting tablet forms a gel when combined with the volume of water necessary to dissolve the drug; this formulation thus reduces the extractability of the drug from the tablet. It should be noted that although these compositions preclude abuse by injection, this approach fails to prevent abuse by crushing and swallowing or snorting the formulation, which are commonly reported methods of abuse associated with OxyContin®.
U.S. Pat. Nos. 3,773,955 and 3,966,940 describe formulations containing a combination of opioid agonists and antagonists, in which the antagonist does not block the therapeutic effect when the admixture is administered orally, but which does not produce analgesia, euphoria or physical dependence when administered parenterally by an abuser. U.S. Pat. No. 4,457,933 describes a method for decreasing both the oral and parenteral abuse potential of strong analgesic agents by combining an analgesic dose of the analgesic agent with an antagonist in specific, relatively narrow ratios. U.S. Pat. Nos. 6,277,384, 6,375,957 and 6,475,494 describe oral dosage forms including a combination of an orally active opioid agonist and an orally active opioid antagonist in a ratio that, when delivered orally, is analgesically effective but that is aversive in a physically dependent subject. While such a formulation may be successful in deterring abuse, it also has the potential to produce adverse effects in legitimate patients.
It is therefore an object of the present invention to provide a pharmaceutical composition that significantly reduces the potential for improper administration or use of drugs but which, when administered as directed, is capable of delivering a therapeutically effective dose.